Optocoupler devices (or optcouplers) contain at least one optical emitter device (or component) which is optically coupled to an optical receiver device (or component) through an optically transmissive medium. This arrangement permits the passage of information from one electrical circuit that contains the optical emitter device to another electrical circuit that contains the optical receiver device. A high degree of electrical isolation is maintained between the two circuits. Because information is passed optically across an insulating gap, the transfer is one way. For example, the optical receiver device cannot modify the operation of a circuit containing the optical emitter device. This feature is desirable because, for example, the emitter may be driven by a low voltage circuit using a microprocessor or logic gates, while the output optical receiver device may be part of a high voltage DC or AC load circuit. The optical isolation also prevents damage to the input circuit caused by the relatively hostile output circuit.
FIG. 1 shows a side view of a conventional optocoupler package 10. The illustrated optocoupler 10 includes a substrate 24, and solder balls 18 on the substrate 24. An LED (light emitting diode) device 16 including an optical emitter surface 16(a) and a phototransistor device 12 (including an optical receiver surface 12(a)) are on the substrate 24 and are covered by an optically transmissive medium 22.
The output current generated by phototransistor (diode) device 12 is low (e.g., about several nA, the same level as noise) due to the low efficiency of the phototransistor 12 device to receive very limit light emitting by LED. This requires the optocoupler package to have very good electrical performance. However, due to the layout of conventional optocoupler package and its bond wires, the noise of the conventional design can induce a noise level which has the same or even greater than the output current. In addition, the size of conventional optocoupler packages can be hard to reduce due to the bond wire and pre-molded structures. This can limit its application to new generation of electronic products which require an ultra-thin and small size.